Phased array transmitters are composed of a typically regular two-dimensional array of radiating or transmission elements. Each of these elements typically has an associated phase shifter. Beams are formed by shifting the phase of the signal emitted by each of the radiating elements. The result is constructive and destructive interference in the far field that enable the steering of the beam.
The same principle can be applied to phased array receivers. Similarly, a two-dimensional array of antenna or detection elements receives the incoming radiation. Their corresponding phase shifters shift the relative phase of the signals from each of the detection elements in order to create the constructive interference based on the incoming signal's angle of incidence on the receiver.
Traditionally, phased array systems have been common in RADAR systems. These systems operate in the radio frequency regime, in the MegaHertz to GigaHertz frequencies. More recently, optical phased array systems are being proposed and built.
Two common applications for optical phased array systems are communication and LiDAR. Phased array transmitters in optical communications systems enable the optical beam, encoding the desired information, to be steered toward and track the receiver. At the same time, a phased array receiver can direct the gain at the desired optical signal. Such systems can be used for the secure transmission of information with lower power requirements. On the other hand, LIDAR (light radar) is typically a surveying or tracking method that measures the distance to a target with laser light by measuring the reflected pulses. The key advantage to using phased array transmitters and receivers in both of these applications is that the optical signal can be scanned very quickly and precisely, electronically.
One characteristic of phased array antenna systems is the generation of unwanted grating lobes. These are caused by the how the optical signal spreads out from the transmitter elements, and creates constructive interference at angles other than the desired path. A similar process occurs in receivers.
The amplitude of the grating lobes is significantly affected by pitch size, i.e., spacing, between the radiation/detection elements, the number of radiating/detection elements, frequency operation, and bandwidth. In general, grating lobes will occur whenever the pitch size is equal to or greater than the wavelength, and there will be no grating lobes when pitch size is smaller than half a wavelength. The lobes are also affected by steering angle.